1. Field of the Invention
The present invention relates to an optical transmitter using a thermoelectric module for regulating a temperature of a light emitting device.
2. Related Background of the Invention
In order to stabilize performance of a light emitting device such as a laser diode (LD), there has been known an optical transmitter having a thermoelectric element for adjusting a temperature of the LD (e.g., cf. Japanese Patent Application Laid-Open No. 9(1997)-27655).
The optical transmitter disclosed in the above-mentioned document comprises a thermoelectric module, and the thermoelectric module comprises a first substrate having a substantially circular shape, a second substrate having a larger diameter than the first substrate, and an electronic element to be arranged between the both substrates. An optical semiconductor module is mounted on the first substrate. Stabilization of output wavelength of the optical transmitter is enhanced by the above-described configuration.
However, the thermoelectric module disclosed in the above-mentioned document requires high electric power. An object of the present invention is to provide an optical transmitter configured to reduce electric power consumption of a thermoelectric module therein.
The increase in the electric power consumption by the thermoelectric module in the conventional optical transmitter may be attributed to the fact that many devices including a light emitting device, a thermistor, monitor photodiode (mPD), and the like were placed on the substrate of the thermoelectric module. That is, the devices mounted on the substrate stores the heat even in a idling state (before starting the thermoelectric module), and heat quantity is proportional to the volume of the mounted devices. Accordingly, the heat quantity to be stored is increased when the volume is increased. When the thermoelectric module is started, it is necessary to adjust the temperature appropriately to control the light emitting device while compensating the heat quantity which was stored in the idling state to begin with. However, when there are many devices mounted on the substrate, much quantity of heat should be compensated accordingly. Such heat compensation causes the increase in the electric power consumption.
Moreover, an device to be driven by electric signals, such as the mPD, is connected to a lead terminal via a wire and the like. Accordingly, the outside heat flows into the package through the lead terminal and the wire. Therefore, the compensation of the heat from the outside further causes the increase in the electric power consumption. In the meantime, the mPD needs to be disposed in the vicinity of the light emitting device so as to receive the light outputted therefrom.
As shown in FIG. 5, there is also disclosed an optical transmitter which removes an mPD 104 from a first plate member 101. However, this optical transmitter requires a prism mirror 108, a condenser lens (not shown), and the like to be disposed on the substrate 101 in order to guide light outputted from a light emitting device (LD) 105 to the mPD 104. Therefore, this optical transmitter dose not reduce the number of materials subject to heat absorption. Moreover, there are also problems of an increase in size of the module, deterioration in coupling efficiency caused by an increase in optical path length between the LD and the mPD, and the like. Based on the above-described disclosure, it may be necessary to reduce the number of devices placed on the substrate and thereby to reduce the power consumption.